Many industries rely on communication between separated devices for data transfer wherein the data transferred may include, but is not limited to, sensor readings, safety and control commands, and status information. It is common that such communications are carried over communication channels wherein unwanted noise impairs the reception of the data.
As one example, and not intended as a limitation, the petroleum industry relies heavily on the operation of drilling into the earth, both on land and offshore, in the exploration for and production of petroleum products. Over the years, the more readily found and accessible petroleum reservoirs have of course been discovered and depleted first. As a result, the exploration and production operations must necessarily concentrate to a greater degree on less accessible and less readily discoverable reserves. In order to reach these locations, the depths of drilling have increased, the locations at which drilling takes place have become increasingly difficult and less accessible, and the drilling operations have necessarily become more complex. Accordingly, drilling operations in the search for and production of petroleum products have become more expensive, with this trend likely to continue in the future. Because of this increasing cost, the accuracy and efficiency of the drilling operation is becoming even more important.
The success and efficiency of the drilling operation depends to a large degree on the quantity and quality of information that the drilling operator has about the sub-surface structure into which the drilling is taking place, and also about parameters concerning the operation of the drill bit as it proceeds into the earth. Many techniques for acquisition and communication of such information have been tried and used in the industry. Examples of such telemetry systems include fluid acoustic and mud pulse telemetry that both use the drilling fluid as a transmission medium, electromagnetic (EM) telemetry through the earth, and acoustic stress-wave telemetry using the drill string material as a transmission medium. In general, the oil drilling industries need is to effectively increase data transmission rates to accommodate the ever increasing amount of measured downhole data. Common transmission rates to date are in the range of 2-10 bits per second. Desirable data rates using the techniques described are on the order of 100-1000 bits per second. Typically, in these transmission systems, the received data signal is, at best, of the same order of magnitude as the noise. At higher transmission rates, the signal-to-noise ratio (SNR) will be substantially less than one.
In any transmission system, a wide collection of unknown possible noise sources are likely to exist. These noises are most troubling if of the same nature (frequency and phase) and magnitude as the planned transmission. That is, for example, if the transmission mode is EM then stray electrical noise is likely to be added to the transmitted signal. If the transmission mode is acoustic, then mechanical and other vibration related noise will be in the signal stream. If the transmission is mud pulse, then pump pulsations and fluid turbulence generated pulsations may be added to the signal. For the most part, these and other random noises are always present and can not be prevented from entering the data signal, therefore a technique to remove them at the receiving end is of great interest.
The electrical noise is likely to come from within and outside the above discussed elements. Electric noise from within is likely to be transmitted as part of the ‘data’ stream while external electrical noise is likely to simply appear in the ‘data’ stream from outside sources.
Acoustic system will be prone to the same internal noise issue and the electrical noise maybe transmitted as part of the projected signal. Like external electrical noise, external mechanical noise or vibration may be super imposed on to the data stream.
Other applications experience similar noise problems. For example, transmission between production devices in a well and either subsurface or surface located controllers may be hampered by noise. Likewise, multiple production systems in multiple wells may be used to produce a single reservoir or multiple reservoirs in a certain area. The multiple control systems may be interlinked to a common controller to enhance production. Such systems may be linked, for example, by hardwire or radio frequency systems that experience noise in the communication channels. Another application includes sub-sea acoustic safety communication for control of subsurface safety valves in case of a loss of other communication capabilities.
In general, for such telemetry systems, the receiving system will need to be able to remove these noise signals from the data stream. There is a demonstrated need for a system and method for extracting data signals from relatively high noise communication paths.